1. Field of the Invention
The present invention relates to a noise filter which is suitable for use in suppression of electromagnetic noise interferences in electronic devices.
2. Description of the Related Art
In general, various types of noise filters are used in suppression of electromagnetic noise interferences in electronic devices. In a known related art noise filter, for example, a circuit using a lumped constant such as a three-terminal capacitor is formed (see for example, Japanese Unexamined Patent Application Publication No. 10-154632 ). In such a noise filter of the related art, noise is suppressed using a reflection loss in which the reflection coefficient is increased at the frequency of noise to be generated.
Moreover, in a known noise filter according to another related art, a circuit including many inductors and capacitors is formed (see for example, Japanese Unexamined Patent Application Publication No. 2000-34894 ).
According to the above-mentioned related art techniques, noise is suppressed by use of the reflection loss. In the case where a noise filter is disposed, e.g., in a line connecting circuits to each other, problems are caused in that probably, noise having a specific frequency resonates between the noise filter and a circuit in the periphery thereof, and the resonance causes amplification of the noise.
Especially, in recent years, signal frequencies to be adapted for digital devices tend to become higher, and the number of electronic devices of which the signal frequencies exceed 100 MHz has been increased. Therefore, low-pass filters of which the cut-off frequencies exceed 200 MHz have been demanded. On the other hand, for example, the lengths of lines between a noise filter and parts disposed in the periphery thereof and the lengths of lines between plural parts are such that resonance with a signal (noise) with a high frequency of 200 MHz or higher may occur easily. Accordingly, for electronic parts of which the signal frequencies exceed 100 MHz, noise filters using reflection loss as carried out in the related art ones are difficult to be used.
Moreover, according to the other related art, resonance phenomena are suppressed by reduction of the reflection loss. However, in the noise filter of the other related art, many inductors and capacitors are connected to form a circuit. The structure is complicated, the size can be reduced with much difficulty, and the manufacturing cost is high. Moreover, problematically, the noise filter is difficult to be fixed to a printed wiring, since the filter has no chip-shape.
In view of the above-described problems of the related art, the present invention has been devised. An object of the present invention is to prevent noise from resonating and provide a noise filter which is small in size and inexpensive.